The present invention corresponds to the generally known prior art that radio vehicle keys which transmit a radio signal to a vehicle and cause the central locking system, provided in the vehicle, to lock or to unlock the vehicle doors and the trunk are used for opening and closing vehicles. In this context, it is provided in a typical manner that the opening and closing of the motor vehicle is indicated by a visual or audible acknowledgement signal. Frequently, the flashing indicators of the vehicle are activated once or twice. In some cases, a quiet sound signal is also generated which is perceived in the immediate vicinity of the vehicle and signals to the driver that the closing process has been carried out successfully. Under certain circumstances, these signals also assist in finding the motor vehicle in large car parks. However, neither the flashing indicator signals nor the audible signals can be perceived so well that they reliably facilitate the finding of the vehicle.
It is also known to trigger by means of the vehicle key a radio signal which does not initiate a closing process but activates the horn of the vehicle. As a rule, the horn signal is so loud that it can be easily perceived and the vehicle can thus be found in a simple manner. However, the horn signal may disturb other road users considerably. In closed spaces (such as multistory car parks) or in inner cities, horn-blowing is frequently not permitted at all for this reason.
DE 10 2005 035 242 A1, which is incorporated by reference, describes a system for multi-purpose traffic surveillance by using a multiplicity of sensors, by means of which a vehicle is monitored in individual or staggered route sections in order to detect, to document and to punish violations of the road traffic regulations. Using these systems, it may also be possible to find a parked vehicle. However, this would require almost area-wide coverage with these surveillance systems which is neither desirable nor feasible.
From DE 696 10 626 T2, which is incorporated by reference, a method and a module for communicating with an object and/or for observing and especially locating a vehicle are known which are used for finding a motor vehicle again both in the close vicinity and, for example, after a theft, in a simple manner and by means of known technical systems. For this purpose, it is proposed to use three systems simultaneously for locating: a large-area paging network (paging services), a cellular mobile radio network and a local area network with band-spreading transmission method (code division multiple access network) which are coupled in a system provided in the vehicle. The large-area paging network is used for the major part of the communication and thus preserves the capacity of the mobile radio network. The cellular mobile radio network is used for bidirectional communication with the vehicle. The third network comprises a receiver which can reliably receive data e.g. from a receiving beacon and send back data to a local receiver. This third network is used, in the case of a theft, for sending data to the moving vehicle which then attracts attention, for example by audible and/or visual signals, or deactivates vehicle functions. However, such a system is not suitable for facilitating, for example, the finding of the vehicle in a large car park since the accuracy is not sufficient and the technical means are too complex.
In some cases, it is also known to integrate suitable locating functions in other mobile devices such as mobile telephones or PDAs. However, this requires that the driver of the vehicle always carries this additional device. In addition, separate technical setting-up of the additional device is necessary which is frequently found to be complex and susceptible to faults especially in modern mobile devices.